synapses

Question 1

what is a synapse?

Answer 1

gaps between axon end of one neurone and dendrite of an adjacent neurone

Question 2

how are synapses involved in action potentials?

Answer 2

the action potential is transmitted as a neurotransmitter which diffuses across a synapse

Question 3

what does the axon terminal button contain?

Answer 3

• vesicles containing neurotransmitters
• neurotransmitter reuptake pump
• gated Ca2+ channels

Question 4

why are impulses at synapses unidirectional?

Answer 4

• neurotransmitters are only released from presynaptic neurones
• receptors for neurotransmitters are only on post synaptic neurones
• so neurotransmitters can only activate action potentials in the post synaptic neurone

Question 5

what is a neuromuscular junction?

Answer 5

the synapse between a motor nerve and a muscle

Question 6

what is a sarcolemma?

Answer 6

plasma membrane which surrounds a muscle cell

Question 7

what is the motor end plate?

Answer 7

the part of the sarcolemma which faces the synapse

Question 8

how does transmission work at a neuromuscular junction?

Answer 8

• action potential reaches neuromuscular junction
• vesicles of acetylcholine fuse with presynaptic membrane
• acetylcholine diffuses across synapse and binds with receptors of post synaptic neurone
• allows Na+ to enter muscle which brings about contraction

Question 9

what is divergence?

Answer 9

one neurone releases neurotransmitters to many neurones

Question 10

what is convergence?

Answer 10

many neurones release neurotransmitters to one neurone

Question 11

what is an excitatory post synaptic potential?

Answer 11

• action potential passes down axon to synapse
• causes a few vesicles to move and fuse with pre synaptic membrane
• small number of acetylcholine molecules produces small depolarisation
• alone not sufficient enough to cause action potential

Question 12

what is summation?

Answer 12

the combined effect of several EPSPs to increase membrane depolarisation to reach threshold and cause action potential

Question 13

what is spatial summation?

Answer 13

when two or more presynaptic neurones converge and release neurotransmitters at the same time onto the same post synaptic neurone
- small amount released from each can be enough altogether to reach threshold and trigger action potential

Question 14

what is temporal summation?

Answer 14

when two or more nerve impulses arrive in quick succession from same presynaptic neurone
- action potential is more likely because more NT is released into synapse